1. Field of the Invention
This invention generally relates to radiation therapy for treating restenosis. More particularly, this invention relates to a device for irradiating a stenosed region of an artery by means of a radiation source.
2. Brief Description of Related Art
The treatment of restenosis after angioplasty using radiation is well known. Angioplasty (also referred to as percutaneous transluminal angioplasty (PTA)), is a non-surgical technique for unblocking vascular lumens resulting from peripheral and coronary vascular disease. This technique has become an accepted form of treatment in both the United States and internationally. Another form of treating vascular disease is atherectomy, which involves the removal of stenotic lesions from arteries by means of a cutting tool.
In typical angioplasty procedures, a guiding catheter is percutaneously introduced into the vascular system of a patient's body through an artery. Once inserted, the guiding catheter is maneuvered through the vascular artery until the distal tip of the guiding catheter is positioned proximal to the lesion site. A balloon catheter and a guide wire are then introduced through the guiding catheter. First, the guide wire is advanced through the distal tip of the catheter until the distal end of the guide wire moves past the lesion to be dilated. Then, the balloon catheter is advanced over the guide wire to a location such that the balloon is positioned inside the atherosclerotic narrowing of the artery. The angioplasty procedure may then begin by inflating the balloon to a predetermined size, thereby compressing the atheroma. This enlarges the atherosclerotic narrowing and enlarges the lumen by stretching the vessel wall. After a predetermined period of time, the balloon is deflated, completing a portion the procedure.
However, a recurrent problem following angioplasty or atherectomy is that excessive tissue growth may occur at the site of the treated lesion, thereby causing the development of further blockage or renarrowing of the diseased vessel. This problem, called restenosis, is thought to be part of the natural healing process after stretching the vascular structure during angioplasty. It is caused by fibrointimal proliferation of the stretched wall in which the cells lining the vascular interior multiply and form fibrous tissue. Restenosis can result in the necessity of repeating the angioplasty or atherectomy procedure.
The use of radiation therapy to prevent the growth of such fibrous tissue after an angioplastic or atherectomy procedure, thereby reducing the tendency for restenosis, is well known. The following United States Letters Patents disclose various embodiments for such irradiation treatment: U.S. Pat. No. 5,199,939 to Dake et al., U.S. Pat. No. 5,302,168 to Hess, U.S. Pat. No. 5,354,257 to Roubin et al. and U.S. Pat. No. 5,411,466 to Hess, which are incorporated in their entireties herein by reference. The devices in each of the foregoing patents expose a stenosis site to radiation by providing a carrier, e.g., a catheter and/or guide wire, which includes a radiation source and advancing the carrier in order to deliver the radiation source to the treatment site. In addition, the Dake patent discloses the use of a liquid, gas or powder radioactive source separate from a carrier. None of the aforementioned patents teaches delivering the radiation source by first positioning the carrier, then inserting a sliding pellet or sleeve type radiation source into or onto the carrier and applying a mechanical or hydraulic force in order to deliver the source to the stenosis site. Accordingly, for irradiation using a non-liquid or gas radiation source, each of the devices (and the methods for using such devices) taught in the U.S. Patents referenced above necessitate the insertion of a carrier provided with the radiation source.
There are several shortcomings of the prior art devices and methods which we have identified. For example, at the appropriate time for the irradiation procedure, the carrier provided with the radiation source must be precisely placed at the stenosis site. The physician performing the procedure accomplishes such precise placement by maneuvering the proximal end of the carrier in order to move its distal end. The physician views the placement of the carrier using fluoroscopic imaging. With the radiation source permanently provided at the distal end of the carrier, the precise placement of the carrier is critical because should an error occur in placing the radiation, the success of the procedure can be jeopardized, healthy tissue can be improperly irradiated and the length of time to successfully complete the procedure can be increased. More particularly, misplacing the source even slightly from the lesion site can result in improper irradiation of the site since the period of time which the source must remain in place is dependent upon its distance from the lesion site walls. Also, misplacing the source from the lesion site can result in irradiating another segment of the vascular artery, thereby exposing healthy tissue to unnecessary radiation.
Another shortcoming of the prior art devices and methods involves integrating the carrier and the radiation source into one device for use in the procedure. Namely, integrating separate components increases the rigidity of the device. This impacts the physician's ability to track the device through the tortuous arteries because greater rigidity makes maneuvering the device more difficult. Where a malfunction renders either the carrier or the source unusable, the procedure must be interrupted, and a new integrated device must be used. For example, should kinking occur in either the guide wire and/or catheter during insertion into vascular arteries, the entire integrated device may be affected. Kinking of the integrated carrier device can cause the misplacement problems described above and cause the patient to be exposed to the radiation source or an unnecessary period of time. Moreover, where the carrier must be replaced due to kinking or another malfunction, the radiation source will not be used for its intended purpose because it will be discarded along with the catheter. Similarly, where the radiation source is defective, the catheter and/or guide wire is rendered unusable. Accordingly, where these complications occur, the irradiation procedure will be delayed or unsuccessful.
Another disadvantage associated with a device in which a carrier and a radiation source are integrated is that the device must be specially manufactured. Given the number of variations in both catheters and guide wires, adding a radioactive source to such carriers not only increases the manufacturing cost but adds to the complexity of the device which can result in an increase in the cost and complexity of the irradiation procedure itself. Once constructed, the added complexity of the carriers increases the chance that the carrier and/or radiation source will malfunction.
During use, where any of the above malfunctions or complications occurs, the period of time that the radiation source is present in the patient's body as well as the length of time required to successfully complete the irradiation procedure will be increased. This results in increasing the patient's exposure to medical risks inherent in the irradiation procedure as well as more general medical procedure risks. The likelihood of additional complications for the patient is thereby also increased.
Accordingly, there is a need to improve the devices heretofore known for irradiating a stenosis site, in order to overcome the above described shortcomings in the known devices and methods.